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Customer details specificationλ︎

Create a new file for the specifications, src/practicalli/banking_specifications.cljc, with the namespace practicalli.banking-specifications.

Require the clojure.spec.alpha library with an alias of spec.

(ns practicalli.banking-specifications
  (:require [clojure.spec.alpha :as spec]))

Define basic customer detailsλ︎

Define a specification for the customer-details map, composed of all the required keys that define a customer.

The bank legally requires specific information about a customer in order to add them as an account holder

(spec/def ::first-name string?)
(spec/def ::last-name string?)
(spec/def ::email-address string?)

INFO::A more detailed email specificationλ︎

Use a regular expression to define the syntax of an email address, eg.

(spec/def ::email-address
  (spec/and string?
            #(re-matches #"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,63}$"

This specification will require a custom generator

A residential address is made from several pieces of information and is defined as a composite specification, from several specifications.

(spec/def ::house-name-number (spec/or :string string?
                                       :number int?))
(spec/def ::street-name string?)
(spec/def ::post-code string?)
(spec/def ::county string?)
(spec/def ::country string?)
(spec/def ::residential-address (spec/keys :req [::house-name-number ::street-name ::post-code]
                                           :opt [::county ::country]))

A social security number specification is also a candidate for a composite specification. Social security numbers may take different forms and even have different names in different countries, eg. the USA SSN is a nine-digit number in the format "AAA-GG-SSSS"

In the UK the social security number is called the National Insurance number and is of the form QQ123456C

(spec/def ::social-security-id-uk string?)
(spec/def ::social-security-id-usa string?)

INFO::Detailed social security numbers would check the different formsλ︎

Predicate functions can be defined to check for the size of the different social security forms.

(defn social-security-number-usa? [value] (= 9 (count value)))
(defn social-security-number-uk? [value] (= 11 (count value)))
(spec/def ::social-security-id-usa (spec/and string? social-security-number-usa?))
(spec/def ::social-security-id-uk (spec/and string? social-security-number-uk?))

These specifications required a custom generator in order to produce correct data each time.

A general social security specification can now be defined, with one of any of the country specific specifications

(spec/def ::social-security-id (spec/or ::social-security-id-uk

Composing the customer details specificationλ︎

A customer details specification is a hash-map of key value pairs. The keys are the specifications that have just been defined.

spec/keys creates a specification for a hash-map with required and optional keys. spec/keys also includes a check for a map, so no explicit check for a map is required.

(spec/def ::customer-details
    :req [::first-name ::last-name ::email-address ::residential-address ::social-security-id]))